Abstract

Inverse light transport seeks to undo global illumination ef- fects, such as interreflections, that pervade images of most scenes. This paper presents the theoretical and computational foundations for inverse light transport as a dual of forward rendering. Mathematically, this du- ality is established through the existence of underlying Neumann se- ries expansions. Physically, we show that each term of our inverse series cancels an interreflection bounce, just as the forward series adds them. While the convergence properties of the forward series are well-known, we show that the oscillatory convergence of the inverse series leads to more interesting conditions on material reflectance. Conceptually, the inverse problem requires the inversion of a large transport matrix, which is impractical for realistic resolutions. A natural consequence of our the- oretical framework is a suite of fast computational algorithms for light transport inversion – analogous to finite element radiosity, Monte Carlo and wavelet-based methods in forward rendering – that rely at most on matrix-vector multiplications. We demonstrate two practical applica- tions, namely, separation of individual bounces of the light transport and fast pro jector radiometric compensation to display images free of global illumination artifacts in real-world environments.